In stratum radiatum of CA1, CRFR1-SIG particles were found on the plasma membrane (chevron, A) or in the cytoplasm (arrow, B) of dendritic spines contacted by unlabeled terminals (uT). In A, the labeled spine emanates from a dendritic shaft (D). In stratum lucidum of CA3, CRFR1-SIG particles were found on the plasma membrane (chevron, C) or in the cytoplasm (arrow, D) of dendritic spines contacted by mossy fiber terminals (mT). Scale bar = 500 nm.